Human neutrophils and monocytes are attracted to sites of inflammation and engulf invasive microorganisms or host cell debris. These phagocyte responses are mediated by surface receptors for a variety of substances released by infective agents or host, or derived from host plasma. The purpose of this project is to define the biochemical structure and transduction mechanisms of some of these surface receptors. More specifically, the present studies focus upon: (i) the receptor for bacterially derived formyl peptides, the formyl peptide chemotactic receptor (FPCR); (ii) the receptor for the particle-adherent C3 complement fragment iC3b (CR3); (iii) the pertussis toxin inhibitable GTP binding regulatory protein (Gi) in neutrophils required for FPCR and other receptor mediated cellular responses. Using affinity labeling of FPCR in conjunction with enzymatic cleavage or metabolic inhibitors we have shown that this receptor is highly N-glycosylated containing both complex- and high mannose-type polysaccharides. The polypeptide portion of FPCR appears to be of similar molecular weight with a similar proteolytic cleavage pattern in different phagocytic cells. N-glycosylation of FPCR is not required for ligand binding or stimulus-response coupling to occur. Using antibodies directed at different GTP regulatory proteins, we have shown that the Gi in neutrophils is immunologically distinct from the homologous protein in brain. Using immunogold labeling of CR3 we have shown by electron microscopy that average density of surface CR3 doubles after stimulation with phorbol myristate acetate and that these receptors are clustered on the cell surface. This arrangement may be important for the neutrophil adherence mediated by this receptor.